New Publication: Investigation of magnetic droplet solitons using x-ray holography with extended references

Anja Roeding Latest publications

Congratulations to Erick Burgos-Parra for his recent Scientific Reports publication on the investigation of magnetic droplet solitons using x-ray holography with extended references: https://www.nature.com/articles/s41598-018-29856-y

A dissipative magnetic soliton, or magnetic droplet, is a structure that has been predicted to exist within a thin magnetic layer when non-linearity is balanced by dispersion, and a driving force counteracts the inherent damping of the spin precession. Such a soliton can be formed beneath a nano-contact (NC) that delivers a large spin-polarized current density into a magnetic layer with perpendicular magnetic anisotropy. Although the existence of droplets has been confirmed from electrical measurements and by micromagnetic simulations, only a few attempts have been made to directly observe the magnetic landscape that sustains these structures, and then only for a restricted set of experimental parameter values. In this work we use and x-ray holography technique HERALDO, to image the magnetic structure of the [Co/Ni]x4 multilayer within a NC orthogonal pseudo spin-valve, for different range of magnetic fields and injected electric currents. The magnetic configuration imaged at −33 mA and 0.3 T for devices with 90 nm NC diameter reveals a structure that is within the range of current where the droplet soliton exist based on our electrical measurements and have it is consistent with the expected size of the droplet (∼100 nm diameter) and its spatial position within the sample. We also report the magnetisation configurations observed at lower DC currents in the presence of fields (0–50 mT), where it is expected to observe regimes of the unstable droplet formation.

(a) Set of three coplanar waveguide used for HERALDO. The oval shaped region is the Si3N4 membrane. (b) Zoom of the top section a CPW shown in (a). The red arrow depicts the position where the transversal cut shown in (c). (c) Schematic of a transversal cut along the red arrow in (b) where the position of the nano contact is shown. (d) Schematic of a section of the 16 × 8 μm2 mesa layer containing the nano-contact orthogonal pseudo spin-valve, where the Co/Ni multilayer acts as the free layer and the Co layer as the pinned layer. In this work devices with Cu nano-contacs of 90 and 110 nm diameter were studied. The red arrows indicate the magnetization of the magnetic layers after appliying a magnetic field ranging within 20–3000 mT out-of-plane (blue arrow). (e) Au layer covering one side of the Si3N4 membrane. An aperture of 5 μm diameter and a reference slit of 6 μm in length and ∼60 nm width were milled using a focused ion beam. The pseudo spin-valve is located on the opposite side of the Si3N4 membrane. (f) Schematic set up for HERALDO measurements with an external magnetic field. The sample is positioned in the middle of a portable octupole magnet system (POMS) and the coherent x-rays from the synchrotron source pass through the aperture and the reference slit. The resulting diffraction pattern is captured by a CCD camera at a distance ∼60 cm behind the sample, at the end of the beam-line. The coplanar waveguide (CPW) supplies the DC current that passes through the magnetic layers and generates the STT required to form the droplet soliton.

>> See all XM² publications here: http://emps.exeter.ac.uk/metamaterials/research/publications/ >>

 

 

 

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